This invention relates to an arrangement for measuring, checking and control of the position of, chosen points of bodies with respect to an optical aiming line for accurate measuring of the shape of bodies or of variations of their position or shape with respect to this line and for guiding of bodies along tracks determined with respect to this line.
Actual requirements on measuring and surveying operations in geodesy, in building industries, in transport, in metallurgy, in mining, machinery and in other branches call in a growing degree for such measuring methods, which would allow a full automation for an application in the longest range and with highest accuracy of these operations, i.e. in the first line an automatic registration of the results of measurements or an automatic control of some manufacturing processes according to results of these measurements. Known devices for accurate geodetic measurements are now practically all based on the principle of observation of surveying marks by means of cross lines of optical apparatus of different accuracy where it it possible to provide an automatic reading of angular values or distances, but the human factor influences predominantly the adjustments for each individual measurements, limiting not only the accuracy, but also a full automation of the measurements. Tracing laser beams have been used with success where it is possible to work in a completely homogenous medium with Fresnell optics (vacuum systems of linear accelerators). At common atmospheric conditions the coherent length and thus also the range of similar systems are however reduced to auch an extent, that they loose any practical value. Arrangements using laser beams with conventional optics offer rather problems with parasitic deflection effects and they generally operate with different complicated photoelectric systems for evaluation of the energetic center of the beam, this method being problematical even if stabilized single mode lasers are used. The results obtained with these devices are relatively satisfactory -- it is possible to achieve also a fully automatic evaluation of measurements, but with high requirements on time for these measurements, or with relatively low accuracy, rapidly decreasing with the distance. So far these arrangements should achieve a higher accuracy or some automation of the evaluation, they strictly require at the place of the measured object a relatively demanding and delicate evaluating device, so that they are unsuitable for working under unfavourable conditions. Drawbacks which cannot be overlooked are in addition to the delicacy of the arrangement also the generally high consumption of energy, the size, weight, short life time and relatively high first costs.
The accuracy of these arrangements, the principle of which can be in short characterized as surveying by means of an aiming line in a chosen vertical plane, determined by one point and by an angle, which this line forms with a reference plane (for instance with a horizontal plane), depends of course on the angular stability of the optical axis of the laser or of the telescope with cross lines, which increases its influence with the increasing distance of the measured object. This drawback is substantially reduced at arrangements, using the method of screening the optical beam which is propagated between a transmitter and a receiver -- what can be similarly characterized as surveying by means of an aiming line determined by its two end points.
A number of different arrangements are already known, based on this principle, which is rather convenient, as it allows in a natural way to fully automatize the measurement, there are however different drawbacks, which prevent their application for more accurate surveying. It is above all the not uniform sensitivity and the relatively low accuracy of measurement in different points along the measuring track, a short range of performance, dependence of the accuracy of measurements on variations of the external light conditions or changes of optical properties of the medium along the measuring track, use of mechanical elements (for instance of rotating choppers) and generally also a high consumption of energy and a short life time of the arrangement.